Removal of contaminants from gas streams

ABSTRACT

A process for the removal of contaminants from a gas stream is disclosed. A gas stream is contacted with a chlorine-containing compound to form a mixed gas stream. The mixed gas stream is then contacted with a sorbent in a sorption zone to produce a product gas stream and a sulfur laden sorbent, wherein the sorbent comprises zinc and a promoter metal.

FIELD OF THE INVENTION

The present invention relates generally to contaminant removal from gasstreams. In another aspect, the present invention relates to a processfor removing one or more contaminants from a gas stream via contact witha regenerable sorbent.

BACKGROUND OF THE INVENTION

In recent years, the demand for natural gas and other gas-phase fuelshas increased substantially. At the same time, stricter regulationsconcerning allowable levels of certain components (e.g., sulfur species,acid gases, and other compounds of environmental concern) have beenimposed, prompting fuel gas producers to develop economical methods ofproducing a compliant gas product.

One known method of treating a gas stream to remove undesirablecomponents is to contact the gas stream with a physical or chemicalsolvent. Examples of chemical solvents include amines such asmethyldiethanolamine (MDEA) and diethanolamine (DEA). Often, theselectivity of the chemical solvents can be problematic. For example,while amines are capable of efficiently removing hydrogen sulfide (H₂S)from gas streams, the amines are generally not capable of absorbingother undesirable sulfur-containing compounds, such as, for examplecarbonyl sulfide (COS). As a result, additional process steps (e.g., COShydrolysis) must be carried out before the gas stream can be used asfuel. In addition to removing H₂S, most amines also remove carbondioxide, which can place unnecessary processing loads on subsequentwaste gas facilities. Further, most processes utilizing chemicalsolvents require extensive cooling of the incoming gas stream and oftenuse large volumes of stream to remove absorbed contaminants from thesolvent, which make these processes energy-intensive. Physicalsolvent-based processes are also highly energy-intensive and oftenrequire high operating pressures and/or low operating temperatures.

It has been discovered that a sorbent can be used to treat gas streams.One example of a sorbent that can be used is a sorbent comprising zinc,a promoter metal, and silica. However, if moisture contacts the sorbent,there is a chance that silicates will form. If silicate formation cannotbe controlled or at least limited, then the sorbent would lose most ofits sulfur-scrubbing activity. Excessive loss of activity wouldnecessitate frequent sorbent replacement, rendering the combinedtechnology commercially unviable.

Accordingly, a need exists for a process for limiting the formation ofsilicates when using a sorbent to remove contaminants from a gas stream.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, there is provided a processcomprising, consisting of or consisting essentially of:

a) contacting a gas stream comprising H₂S with a chlorine-containingcompound to form a mixed gas stream;

b) contacting said mixed gas stream with a sorbent in a sorption zone toproduce a first product gas stream and a sulfur laden sorbent, whereinsaid sorbent comprises a metal selected from the group consisting ofzinc, silica, and a promoter metal;

c) drying at least a portion of said sulfur-laden sorbent to therebyprovide a dried sulfur-laden sorbent;

d) contacting at least a portion of said dried sulfur laden sorbent witha regeneration gas stream in a regeneration zone to produce aregenerated sorbent comprising a zinc-containing compound, a silicate,and a promoter metal, and an off-gas stream;

e) returning said regenerated sorbent to said sorption zone to provide arenewed sorbent comprising zinc, silica, and a promoter metal; and

f) contacting said regenerated sorbent with said mixed gas stream insaid sorption zone to form a second product gas stream and a sulfurladen sorbent.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of a contaminant removal system inaccordance with one embodiment of the present invention.

FIG. 2 is a plot of the run/regeneration number vs. the zinc silicateconcentration in weight percent.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a contaminant removal system 10 is illustrated asgenerally comprising a gas source 12, a sorption zone 14, a product gasuser 16, a drying zone 18, a regeneration zone 20, and an off-gas user22. In general, a raw gas stream exiting gas source 12 can be contactedwith a sorbent in sorption zone 14 to thereby remove one or morecontaminants from the gas stream. The resulting, contaminant-depletedproduct gas stream exiting sorption zone 14 can be routed to product gasuser 16, while at least a portion of the contaminant-laden sorbent canbe dried in drying zone 18 prior to being regenerated via contact with aregeneration gas in regeneration zone 20. The resulting off-gas streamexiting regeneration zone 20 can be routed to off-gas user 22, while atleast a portion of the regenerated sorbent can then be returned tosorption zone 14 for subsequent reuse. In one embodiment, at least oneof the sorption, drying, and regeneration zones 14, 18, 20 can becontained within the same process vessel. In another embodiment, atleast one of the sorption, drying, and regeneration zones 14, 18, 20 canbe contained in two or more separate process vessels. Further, thecontaminant removal system 10 depicted in FIG. 1 can be operated incontinuous, semi-continuous, semi-batch, or batch mode. The operation ofcontaminant removal system 10 will now be described in more detailbelow.

Gas source 12 can comprise any source or system capable of producing agas stream. In general, the raw gas stream produced from gas source 12can have a vapor fraction greater than about 0.8, greater than about0.9, or greater than 0.95 at standard conditions. In one embodiment, theraw gas stream from gas source 12 can comprise less than about 1 volumepercent, less than about 0.5 volume percent, less than 0.05 volumepercent, or less than 500 parts per million by volume (ppmv) of C₆+hydrocarbon material. For example, gas source 12 can comprise a naturalgas well, a refinery or chemical plant process stream, or any othersuitable source.

In one embodiment, gas source 12 can comprise a gasification systemoperable to produce a raw gas stream via the gasification of asolid-based carbon-containing material, such as, for example, coal orpetroleum coke. Typically, the solid carbon-containing material can begasified via contact with a gasification stream comprising stream,oxygen, air, hydrogen, carbon dioxide, or any combination thereof. Inone embodiment, a slurry of solid carbon-containing material in conduit100 can be gasified via contact with an oxygen-containing streamentering gas source 12 via conduit 110 at a temperature in the range offrom about 530 to about 1950° C., about 810 to about 1650° C., or 950 to1510° C. and a pressure in the range of from about 150 to about 800pounds-per-square inch, gauge (psig), about 250 to about 700 psig, or300 to 600 psig.

The raw gas stream exiting gas source 12 via conduit 112 can compriseone or more of the following compounds: carbon monoxide (CO), carbondioxide (CO₂), hydrogen (H₂), water (H₂O), propane and lighterhydrocarbons (C₃+), nitrogen (N₂), and the like. Additionally, the rawgas stream can comprise one or more undesirable components (i.e.,contaminants) that should be removed prior to utilizing the raw gasstream as fuel. Sulfur compounds, such as, for example, hydrogen sulfide(H₂S), carbonyl sulfide (COS), carbon disulfide (CS₂), and evenorganosulfur compounds such as mercaptans and various thiopheniccompounds are a few examples of common contaminants found in the raw gasstream. Other examples of contaminants typically present in the raw gasstream can include, but are not limited to ammonia (NH₃), hydrochloricacid (HCl), and hydrogen cyanide (HCN). Table 1, below, summarizes thecomposition of the raw gas stream in conduit 112 according to oneembodiment of the present invention.

TABLE 1 Component in Raw Gas Stream (based on total stream volume)Component Broad Range Intermediate Range Narrow Range H₂ 8-50 vol %10-40 vol % 15-35 vol % CO 10-75 vol % 15-60 vol % 25-50 vol % CO₂ 1-40vol % 5-30 vol % 7-20 vol % H₂O 4-40 vol % 8-30 vol % 10-25 vol % H₂S0.001-5 vol % 0.1-2.5 vol % 0.5-2 vol % CH₄ 0.05-10 vol % 0.1 to 7.5 vol% 0.5 to 5.0 vol % COS 100-5,000 ppmv 200-2,500 ppmv 350-1,500 ppmv HCl50-2,000 ppmv 100-1,500 ppmv 250-1,000 ppmv NH₃ 50-2,000 ppmv 100-1,500ppmv 250-1,000 ppmv Other (total) <2.5 vol % <2.0 vol % <1 vol %

In one embodiment, an additional amount of a chlorine-containingcompound can be added to the raw gas stream before it enters gas source12. The chlorine-containing compound can be selected from the groupconsisting of HCl, an organochloride compound, and combinations thereof.Examples of organochloride compounds that can be used include, but arenot limited to monochloroethane, dichloroethane, trichloroethane,methylchloride, dichloromethane, trichloromethane, tetrachloromethane,monochloroethene, dichloroethene, trichloroethene, and trichlorobenzene.

In an embodiment, the chlorine-containing compound is present in the rawgas stream in an amount in the range of from about 1 ppmv to about 3volume percent. The chlorine-containing compound can also be present inthe raw gas stream in an amount in the range of from about 50 ppmv toabout 1 volume percent. The chlorine-containing compound can also bepresent in the raw gas stream in an amount in the range of from 100 ppmvto 1000 ppmv.

As depicted in FIG. 1, at least a portion of the raw gas stream exitinggas source 12 in conduit 112 can be routed into sorption zone 14,wherein the stream can be contacted with a sorbent to remove at least aportion of at least one contaminant from the incoming gas stream. In oneembodiment, the raw gas stream is not cooled prior to entering sorptionzone 14 and can have a temperature that is within about 200° C., about100° C., or 50° C. of the temperature of the raw gas stream exiting gassource 12. Generally, the raw gas stream entering sorption zone 14 canhave a temperature in the range of from about 150 to about 700° C.,about 250 to about 600° C., or 350 to 450° C. and a pressure in therange of from about 100 to about 750 psig, about 250 to about 600 psig,or 350 to 450 psig.

In general, the sorbent employed in sorption zone 14 can be anysufficiently regenerable zinc-oxide-based sorbent composition havingsufficient contaminant removal ability. While described below in termsof its ability to remove sulfur contaminants from an incoming tail gasstream, it should be understood that the sorbent of the presentinvention can also have significant capacity to remove one or more othercontaminants.

In one embodiment of the present invention, the sorbent employed insorption zone 14 can comprise zinc and a promoter metal component. Thepromoter metal component can comprise one or more promoter metalsselected from the group consisting of nickel, cobalt, iron, manganese,tungsten, silver, gold, copper, platinum, zinc, tine, ruthenium,molybdenum, antimony, vanadium, iridium, chromium, palladium, andmixtures thereof.

In one embodiment, at least a portion of the promoter metal component ispresent in a reduced-valence state. The valence reduction of thepromoter metal component can be achieved by contacting the sorbent witha reducing agent within sorption zone 14 and/or prior to introductioninto sorption zone 14. Any suitable reducing agent can be used,including, but not limited to hydrogen and carbon monoxide.

In one embodiment of the present invention, the reduced-valence promotermetal component can comprise, consist of, or consist essentially of, asubstitutional solid metal solution characterized by the formula:M_(A)Zn_(B), wherein M is the promoter metal and A and B are eachnumerical values in the range of from about 0.01 to about 0.99. In theabove formula for the substitutional solid metal solution, A can be inthe range of from about 0.70 to about 0.98 or 0.85 to 0.95 and B can bein the range of from about 0.03 to about 0.30 or 0.05 to 0.15. In oneembodiment, A+B=1.

Substitutional solid solutions are a subset of alloys that are formed bythe direct substitution of the solute metal for the solvent metal atomsin the crystal structure. For example, it is believed that thesubstitutional solid metal solution M_(A)Zn_(B) is formed by the solutezinc metal atoms substituting for the solvent promoter metal atoms.Three basic criteria exist that favor the formation of substitutionalsolid metal solutions: (1) the atomic radii of the two elements arewithin 15 percent of each other; (2) the crystal structures of the twopure phases are the same; and (3) the electronegativities of the twocomponents are similar. The promoter metal (as the elemental metal ormetal oxide) and zinc (as the elemental metal or metal oxide) employedin the sorbent described herein typically meet at least two of the threecriteria set forth above. For example, when the promoter metal isnickel, the first and third criteria, are met, but the second is not.The nickel and zinc metal atomic radii are within 10 percent of eachother and the electronegativities are similar. However, nickel oxide(NiO) preferentially forms a cubic crystal structure, while zinc oxide(ZnO) prefers a hexagonal crystal structure. A nickel zinc solidsolution retains the cubic structure of the nickel oxide. Forcing thezinc oxide to reside in the cubic structure increases the energy of thephase, which limits the amount of zinc that can be dissolved in thenickel oxide structure. This stoichiometry control manifests itselfmicroscopically in an approximate 92:8 nickel zinc solid solution(Ni_(0.92) Zn_(0.08)) that is formed during reduction andmicroscopically in the repeated regenerability of sorbent.

In addition to zinc and the promoter metal, the sorbent employed insorption zone 14 can further comprise silica and an aluminate. Thealuminate can comprise a promoter metal-zinc aluminate substitutionalsolid solution characterized by the formula: M_(Z)Zn_((1-Z))Al₂O₄,wherein M is the promoter metal and Z is in the range of from 0.01 to0.99. Any silica-containing compound which ultimately increases themacroporosity of the sorbent can be used. In one embodiment, theporosity enhancer can comprise perlite. Examples of sorbents suitablefor use in sorption zone 14 and methods of making these sorbents aredescribed in detail in U.S. Pat. Nos. 6,429,170 and 7,241,929, theentire disclosures of which are incorporated herein by reference.

Table 2, below, provides the composition of a sorbent employed insorption zone 14 according to an embodiment of the present inventionwhere reduction of the sorbent is carried out prior to introduction ofthe sorbent into sorption zone 14.

TABLE 2 Reduced Sorbent Composition (wt %) Range ZnO M_(A)Zn_(B) PEM_(Z)Zn_((1−Z))Al₂O₄ Broad 10-90  5-80 2-50 2-50 Intermediate 20-6010-60 5-30 5-30 Narrow 30-40 30-40 10-20  10-20 

In an alternative embodiment where the sorbent is not reduced prior tointroduction into sorption zone 14, the promoter metal component cancomprise a substitutional solid metal oxide solution characterized bythe formula M_(X)Zn_(Y)O, wherein M is the promoter metal and X and Yare in the range of from about 0.01 to about 0.99. In one embodiment, Xcan be in the range of from about 0.5 to about 0.9, about 0.6 to about0.8, or 0.65 to 0.75 and Y can be in the range of from about 0.10 toabout 0.5, about 0.2 to about 0.4, or 0.25 to 0.35. In general, X+Y=1.

Table 3, below, provides the composition of an unreduced sorbentemployed in sorption zone 14 according to an embodiment where thesorbent is not reduced prior to introduction into sorption zone 14.

TABLE 3 Unreduced Sorbent Composition (wt %) Range ZnO M_(X)Zn_(Y)O PEM_(Z)Zn_((1−Z))Al₂O₄ Broad 10-90  5-70 2-50 2-50 Intermediate 20-7010-60 5-30 5-30 Narrow 35-45 25-35 10-20  10-20 

As mentioned above, when an unreduced sorbent composition is contactedwith a hydrogen containing compound in sorption zone 14, reduction ofthe sorbent can take place in sorption zone 14. Therefore, when sorbentreduction takes place in sorption zone 14, the initial sorbent contactedwith the raw gas stream in sorption zone 14 can be a mixture of reducedsorbent (Table 2) and unreduced sorbent (Table 3).

In general, the incoming raw gas stream can contact the initial sorbentin sorption zone 14 at a temperature in the range of from about 150° C.to about 650° C., about 225° C. to about 550° C., or 325° C. to 475° C.and a pressure in the range of from about 100 to about 750 psig, about250 to 575 psig, or 350 to 450 psig. At least a portion ofsulfur-containing compounds (and/or other contaminants) in the raw gasstream can be sorbed by the sorbent, thereby creating a sulfur-depletedproduct gas stream and a sulfur-laden sorbent. In one embodiment,sulfur-removal efficiency of sorption zone 14 can be greater than about85 percent, greater than about 90 percent, greater than about 95percent, greater than about 98 percent, or greater than 99 percent. Asdepicted in FIG. 1, at least a portion of the contaminant-depletedproduct gas stream can exit sorption zone 14 via conduit 114. In oneembodiment, the product gas stream can comprise less than about 50, lessthan about 20, less than about 10, less than about 5, or less than 1ppmv H₂S.

As shown in FIG. 1, the contaminant-depleted product gas stream can thenbe routed to a product gas user 16. Product gas user 16 can comprise anyindustrial, commercial, or residential use or application of acontaminant-depleted product gas stream. In one embodiment, product gasuser 16 can comprise an industrial gas turbine located in a facilityused to co-produce stream and electricity.

As depicted in FIG. 1, at least a portion of the sulfur-laden sorbentdischarged from sorption zone 14 can be routed to drying zone 18 viaconduit 116. In one embodiment, the sulfur-laden sorbent can have asulfur loading in the range of from about 0.1 to about 27, about 3 toabout 26, about 5 to about 25, or 10 to 20 weight percent. In dryingzone 18, at least a portion of the sulfur-laden sorbent can be dried byflowing an inert gas purge stream in conduit 118 having a temperature inthe range of from about 100 to about 550° C., about 150 to about 500°C., or 200 to 475° C. through the sorbent for a time period of at leastabout 15 minutes, or a time period in the range of from about 30 minutesto about 100 hours, about 45 minutes to about 36 hours, or 1 hour to 12hours. The resulting dried, sulfur-laden sorbent can then be routed toregeneration zone 20 via conduit 120, as illustrated in FIG. 1.

Regeneration zone 20 can employ a regeneration process capable ofremoving least a portion of the sulfur (or other sorbed contaminants)from the sulfur-laden sorbent via contact with a regeneration gas streamunder sorbent regeneration conditions. In one embodiment, theregeneration gas stream entering regeneration zone 20 via conduit 122can comprise an oxygen-containing gas stream, such as, for example, air(e.g., about 21 volume percent oxygen). In another embodiment, theregeneration gas stream in conduit 120 can be an oxygen-enriched gasstream comprising at least about 50, at least about 75, at least about85, or at least 90 volume percent oxygen. In yet another embodiment, theregeneration gas stream can comprise a substantially pure oxygen stream.

According to one embodiment of the present invention, the regenerationprocess employed in regeneration zone 20 can be a step-wise regenerationprocess. In general, a step-wise regeneration process includes adjustingat least one regeneration variable from an initial value to a finalvalue in two or more incremental adjustments (i.e., steps). Examples ofadjustable regeneration variables can include, but are not limited to,temperature, pressure, and regeneration gas flow rate. In oneembodiment, the temperature in regeneration zone 20 can be increased bya total amount that is at least about 75° C., at least about 100° C., orat least 150° C. above an initial temperature, which can be in the rangeof from about 250 to about 650° C., about 300 to about 600° C., or 350to 550° C. In another embodiment, the regeneration gas flow rate can beadjusted so that the standard gas hourly space velocity (SGHSV) of theregeneration gas in contact with the sorbent can increase by a totalamount that is at least about 1,000, at least about 2,500, at leastabout 5,000, or at least 10,000 volumes of gas per volume of sorbent perhour (v/v/h or h⁻¹) above an initial SGHSV value, which can be in therange of from about 100 to about 100,000 h⁻¹, about 1,000 to about80,000 h⁻¹, or 10,000 to 50,000 h⁻¹.

In one embodiment, the size of the incremental adjustments (i.e., theincremental step size) can be in the range of from about 2 to about 50,about 5 to about 40, or 10 to 30 percent of magnitude of the desiredoverall change (i.e., the difference between the final and initialvalues). For example, if an overall temperature change of about 150° C.is desired, the incremental step size can be in the range of from about3 to about 75° C., about 7.5 to about 60° C., or 15 to 45° C. In anotherembodiment, the magnitude of the incremental step size can be in therange of from about 2 to about 50, about 5 to about 40, or 10 to 30percent of magnitude of the initial variable value. For example, if theinitial regeneration temperature is 250° C., the incremental step sizecan be in the range of from about 5 to about 125° C., about 12.5 toabout 100° C., or 25 to 75° C. In general, successive incremental stepscan have the same incremental step sizes, or, alternatively, one or moreincremental step sizes can be greater than or less than the incrementalstep size of the preceding or subsequent steps.

In one embodiment, subsequent adjustments to the regenerationvariable(s) can be carried out at predetermined time intervals. Forexample, adjustments can be made after time intervals in the range offrom about 1 minute to about 45 minutes, about 2 minutes to about 30minutes, or 5 to 20 minutes. In another embodiment, the adjustments canbe made based on the value(s) of one or more “indicator” variable(s). Anindicator variable is a variable in the system monitored to determinethe progress of the sorbent regeneration. Examples of indicatorvariables can include, but are not limited to, sorbent sulfur loading,regeneration sorbent bed temperature, regeneration zone temperatureprofile (i.e., exotherm), and off-gas stream composition. In oneembodiment, the sulfur dioxide (SO₂) concentration in the off-gas streamis monitored to determine when the flow rate of the regeneration gasand/or the regeneration temperature should be incrementally adjusted.

The regeneration process can be carried out in regeneration zone 20until at least one regeneration end point is achieved. In oneembodiment, the regeneration end point can be the achievement of adesired value for one or more of the adjusted regeneration variables.For example, the regeneration process can be carried out until thetemperature achieves a final value in the range of from about 300 toabout 800° C., about 350 to about 750° C., or 400 to 700° C. or theSGHSV reaches a final value in the range of from about 1,100 to about110,000 h⁻¹, about 5,000 to about 85,000 h⁻¹, or 25,000 to 60,000 h⁻¹.In another embodiment, the regeneration process can be finished after apredetermined number of variable adjustments. For example, theregeneration process can be carried out long enough for at least 1 or inthe range of from about 2 to about 8 or 3 to 5 incremental adjustmentsto be made. In yet another embodiment, the regeneration process can becarried out until a final value of the selected indicator variable isachieved. For example, the regeneration process can be carried out untilthe concentration of SO₂ in the off-gas exiting regeneration zone 20declines to a value less than about 1 volume percent, less than about0.5 volume percent, less than about 0.1 volume percent, or less than 500ppmv. Regardless of the specific endpoint selected, the entire length ofthe regeneration process can be less than about 100 hours, or in therange of from about 30 minutes to about 48 hours, about 45 minutes toabout 24 hours, or 1.5 to 12.5 hours.

In one embodiment, the above-described regeneration process can have aregeneration efficiency of at least about 75 percent, at least about 85percent, at least about 90 percent, at least about 95 percent, at leastabout 98 percent, or at least 99 percent. The regenerated sorbent canhave a sulfur loading that is less than about 10 weight percent, or inthe range of from about 0.05 to about 6 weight percent, or 0.1 to 4weight percent.

While not wishing to be bound by theory, it is believed that if tracesof moisture remain from the drying step, then there is a chance ofsilicate formation on the sorbent during the regeneration process. Ifsilicates are present, sorbent degradation can occur.

As illustrated in FIG. 1, at least a portion of the regenerated sorbentin conduit 124 can then be returned to sorption zone 14. The regeneratedsorbent comprises a zinc-containing compound, a silicate, and a promotermetal. As discussed above, in one embodiment, at least a portion of theregenerated sorbent does not undergo a reduction step prior tointroduction into sorption zone. In such an embodiment, the regeneratedbut unreduced sorbent introduced into sorption zone 14 can comprise anunreduced promoter metal component that includes a substitutional solidmetal oxide solution characterized by the formula M_(X)Zn_(Y)O (Seee.g., Table 3, above). While not wishing to be bound by theory, it isbelieved that silicates that were formed on the sorbent during theregeneration step can be converted to metal chlorides on the sorbentduring the subsequent contacting phase due to the presence of achlorine-containing compound in the raw gas stream. During subsequentregeneration cycles, the chlorine on the sorbent can form chlorineoxides.

Referring back to FIG. 1, the off-gas stream exiting regeneration zone20 via conduit 126 can subsequently be routed to off-gas user 22.Off-gas user 22 can comprise any unit capable of processing the off-gasstream, such as, for example, a Claus sulfur processing unit. In oneembodiment, the off-gas stream exiting regeneration zone 20 via conduit126 can comprise at least about 5, at least about 10, at least about 20,or at least 25 volume percent SO₂. In one embodiment, the off-gas streamcomprises less H₂S than in the tail gas stream entering sorption zone 14via conduit 112. In another embodiment, off-gas stream can comprisesubstantially no H₂S.

EXAMPLE

The following example is intended to be illustrative of the presentinvention and to teach one of ordinary skill in the art to make and usethe invention. This example is not intended to limit the invention inany way.

A sorbent containing nickel, zinc, alumina, and perlite was crushed andsieved to obtain 100+/200-mesh size particles. About 20-30 grams of thecrushed sorbent was combined with the same amount of alundum and theresulting mixture was charged to a fixed bed, downflow reaction vessel.Preheated HCl was added just before a raw gas stream entered thereactor. The raw gas stream, the composition of which is summarized inTable 4 below, was passed through the reaction vessel and contacted withthe sorbent mixture at a temperature of 420° C. and a pressure of 408psig. The simulated raw gas stream was diluted with nitrogen up to about50 volume percent.

TABLE 4 Typical Raw Gas Stream Composition Simulated Feed combinedExperiments Compound (absolute) [vol. %] CO 20.5 H₂ 13.7 CO₂ 8.5 H₂O 9.3H₂S 1.0 COS 0 HCl 300 ppm NH₃ 500 ppm N₂ 47

Water was removed from the depressurized gas before a slipstream wasintroduced to the analytical equipment which included an online massspectrometer (ESS EcoSys Instrument), an online photoacoustics analyzer(INNOVA), and an online micro GC (manufactured by Agilent). The appliedwarm-gas conditions were 420° C. and a pressure of 400 psi. The stepwiseregeneration procedure reached a temperature of 550° C. at atmosphericpressure. The sulfur-laden sorbent was regenerated using air. Prior tothe actual regeneration, hot nitrogen was introduced to dry the sorbentat a temperature of 450° C. and ambient pressure to reduce the potentialfor zinc silicate formation. The regeneration process was a stepwise andalternating increase of temperature and air flow through the sorbent atatmospheric pressure. The regeneration process commenced immediatelyafter the drying process. The temperature was increased stepwise from450° C. to a final temperature of 550° C. in increments of about 30-50°C. The air flow through the sorbent increased from initially about 100mL/min to about 1 L/min in steps of about 100 mL/min to about 250mL/min, so that the gas hourly space velocity (GHSV) slowly increased.

An experiment with 15 cycles (absorption and regeneration) wasconducted. In this experiment, fresh sorbent was not added in betweencycles. A 300 ppmv quantity of HCl was added to the gas stream prior tocontact with the sorbent. FIG. 2 shows the amount of cycles v. thesilicate concentration on the sorbent. The high points are the silicateconcentrations after regeneration. The low points are after thesubsequent contacting phase.

Numerical Ranges

The present description uses numerical ranges to quantify certainparameters relating to the invention. It should be understood that whennumerical ranges are provided, such ranges are to be construed asproviding literal support for claim limitations that only recite thelower value of the range as well as claims limitation that only recitethe upper value of the range. For example, a disclosed numerical rangeof 10 to 100 provides literal support for a claim reciting “greater than10” (with no upper bounds) and a claim reciting “less than 100” (with nolower bounds).

DEFINITIONS

As used herein, the terms “a,” “an,” “the,” and “the” mean one or more.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itselfor any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination; B and C in combination; orA, B, and C in combination.

As used herein, the terms “comprising,” “comprises,” and “comprise” areopen-ended transition terms used to transition from a subject recitedbefore the term to one or more elements recited after the term, wherethe element or elements listed after the transition term are notnecessarily the only elements that make up the subject.

As used herein, the terms “containing,” “contains,” and “contain” havethe same open-ended meaning as “comprising,” “comprises,” and “comprise”provided above. As used herein, the terms “including,” “includes,” and“include” have the same open-ended meaning as “comprising,” “comprises,”and “comprise” provided above.

As used herein, the terms “having,” “has,” and “have” have the sameopen-ended meaning as “comprising,” “comprises,” and “comprise” providedabove.

As used herein, the terms, “including,” “include,” and “included” havethe same open-ended meaning as “comprising,” “comprises,” and “comprise”provided above.

As used herein, the term “indicator variable” refers to a variablemonitored to determine the progress of the sorbent regeneration.

As used herein, the term “reduced-valence promoter metal component”refers to a promoter metal component having a valence with is less thanthe valence of the promoter metal component in its common oxidizedstate.

As used herein, the term “regeneration conditions” refer to conditionsnecessary to remove at least a portion of sorbed sulfur from thesulfur-laden sorbent.

As used herein, the term “regeneration efficiency” refers to the abilityof a regeneration zone to remove one or more sorbed compounds from anincoming sorbent. Regeneration efficiency can be expressed according tothe following formula: [(sulfur loading of sulfur-laden sorbent×mass ofsulfur-laden sorbent entering regeneration zone)−(sulfur loading ofregenerated sorbent×mass of regenerated sorbent exiting regenerationzone)/(sulfur loading of sulfur-laden sorbent×mass of sulfur-ladensorbent entering regeneration zone), expressed as a percentage.

As used herein, the term “sorb” refers to any type or combination ofphysical and/or chemical adsorption and/or absorption.

As used herein, the term “sorbent-damaging compound” refers to acompound sorbed into or onto the sorbent that adversely impacts thesorbent's ability to remove sulfur or other contaminants from a fluidstream.

As used herein, the term “standard conditions” refers to a pressure of 1atmosphere and a temperature of 60° F.

As used herein, the term “standard gas hourly space velocity” or “SGHSV”refers to the gas hourly space velocity of a gas stream measured atstandard conditions.

As used herein, the term “sulfur loading” refers to the average weightpercent of sulfur sorbed onto a sorbent.

As used herein, the term “sulfur removal efficiency” refers to theability of a sorbent to remove sulfur compounds or other contaminantsfrom an incoming fluid stream. Sulfur removal efficiency can becalculated by the following formula: (mass flow rate of sulfur compoundsentering a sorption zone in a fluid stream—mass flow rate of sulfurcompounds exiting a sorption zone in a fluid stream)/(mass flow rate ofsulfur compounds entering a sorption zone in the feed stream), expressedas a percentage.

CLAIMS NOT LIMITED TO THE DISCLOSED EMBODIMENTS

The preferred forms of the invention described above are to be used asillustration only, and should not be used in a limiting sense tointerpret the scope of the present invention. Modifications to theexemplary embodiments, set forth above, could be readily made by thoseskilled in the art without departing from the spirit of the presentinvention. The inventors hereby state their intent to rely on theDoctrine of Equivalents to determine and assess the reasonably fairscope of the present invention as pertains to any apparatus notmaterially departing from but outside the literal scope of the inventionas set forth in the following claims.

1. A process comprising; a) contacting a gas stream comprising H₂S witha chlorine-containing compound to form a mixed gas stream; b) contactingsaid mixed gas stream with a sorbent in a sorption zone to produce afirst product gas stream and a sulfur laden sorbent, wherein saidsorbent comprises a zinc-containing compound, silica, and a promotermetal; c) drying at least a portion of said sulfur-laden sorbent tothereby provide a dried sulfur-laden sorbent; d) contacting at least aportion of said dried sulfur laden sorbent with a regeneration gasstream in a regeneration zone to produce a regenerated sorbentcomprising a zinc-containing compound, a silicate, and a promoter metal,and an off-gas stream; e) returning said regenerated sorbent to saidsorption zone to provide a renewed sorbent comprising zinc, silica, anda promoter metal; and f) contacting said renewed sorbent with said mixedgas stream in said sorption zone to form a second product gas stream anda sulfur laden sorbent.
 2. A process in accordance with claim 1 whereinsaid promoter metal is nickel.
 3. A process in accordance with claim 1,wherein said sorbent comprises a substitutional solid metal solutioncharacterized by the formula M_(A)Zn_(B), wherein M is said promotermetal, wherein A and B are in the range of from about 0.01 to about0.99.
 4. A process in accordance with claim 1, wherein said regeneratedsorbent returned to said sorption zone in step (e) comprises asubstitutional solid metal oxide solution characterized by the formulaM_(X)Zn_(Y)O, wherein M is said promoter metal, wherein X and Y are inthe range of from about 0.01 to about 0.99.
 5. A process in accordancewith claim 1, wherein said gas stream comprises in the range of fromabout 0.001 to about 5 volume percent H₂S.
 6. A process in accordancewith claim 1, wherein said product gas stream comprises less than 50ppmv H₂S.
 7. A process in accordance with claim 1 wherein saidchlorine-containing compound is present in said mixed gas stream in anamount in the range of from about 1 ppmv to about 3 volume percent.
 8. Aprocess in accordance with claim 1 wherein said chlorine-containingcompound is present in said mixed gas stream in an amount in the rangeof from about 50 ppmv to about 1 volume percent.
 9. A process inaccordance with claim 1 wherein said chlorine-containing compound ispresent in said mixed gas stream in an amount in the range of from 100ppmv to 1000 ppmv.
 10. A process in accordance with claim 1 wherein saidgas stream further comprises compounds selected from the groupconsisting of carbon monoxide, hydrogen and combinations thereof.
 11. Aprocess in accordance with claim 1 wherein said sorbent is reduced witha reducing agent in a reduction zone prior to said contacting of saidgas stream in step (a).
 12. A process in accordance with claim 11wherein said reducing agent comprises an agent selected from the groupconsisting of hydrogen and carbon monoxide.
 13. A process in accordancewith claim 1 wherein said gas stream further comprises a reducing agent.14. A process in accordance with claim 13 wherein said reducing agentcomprises an agent selected from the group consisting of hydrogen andcarbon monoxide.
 15. A process in accordance with claim 1 whereinconditions in said sorption zone include a temperature in the range offrom about 150° C. to about 1000° C.
 16. A process in accordance withclaim 1 wherein conditions in said sorption zone include a temperaturein the range of from about 250° C. to about 700° C.
 17. A process inaccordance with claim 1 wherein conditions in said sorption zone includea temperature in the range of from about 350° C. to about 550° C.
 18. Aprocess in accordance with claim 1 wherein conditions in said sorptionzone include a pressure in the range of from about atmospheric pressureto about 5000 psig.
 19. A process in accordance with claim 1 whereinconditions in said sorption zone include a pressure in the range of fromabout atmospheric pressure to about 1000 psig.
 20. A process inaccordance with claim 1 wherein conditions in said regeneration zoneincludes a regeneration gas stream.
 21. A process in accordance withclaim 20 wherein said regeneration gas stream comprises oxygen.
 22. Aprocess in accordance with claim 20 wherein said regeneration gas streamcomprises air.
 23. A process in accordance with claim 1 wherein saidoff-gas stream comprises H₂S.
 24. A process in accordance with claim 23wherein said offgas stream is recycled to a SO₂ treatment zone.
 25. Aprocess in accordance with claim 24 wherein said SO₂ treatment zonecomprises a Claus unit.